All summer long, Person of Interest fans have dealt with one lingering question after last season’s so-good-it’s-maddening finale: Where are Finch, Reese and the rest of Team Machine supposed to go now?

With the library dismantled and the team now underground, Tuesday’s episode finally held the answer to the gestating question, revealing the whereabouts (well, vaguely) of the brand-new headquarters that will now serve as the meeting place for our newly displaced heroes. Viewers got their first peek at the new HQ—an abandoned subway station deep underneath New York City, far from the prying eyes of Samaritan—and EW has an exclusive, closer look at the new digs.

“We’ve been exploring New York for five years, and I don’t think there’s a street corner in the five boroughs that either Greg or myself hasn’t stood on trying to figure out if we could shoot there,” says EP Jonathan Nolan, who, along with EP Greg Plageman, teased EW about what the new headquarters means for the story. “Short of running out of above-ground locations, we got fascinated by the idea that there are these hidden spaces under New York and the quite literal idea that in a panopticon, total surveillance state—like the new one under Samaritan—the only place to go was down.”

With help from his many resources and a little nudging from the Machine, Finch locates an abandoned tunnel, part of a series of empty tunnels and stations that exist in the Metropolitan Transit Authority (now the MTA, formerly the IRT, which eagle-eyed fans will notice allusions to throughout the set). Production designer Rick Butler and his team researched the history of the underground system and concluded that “somewhere in this intricate maze would be a place where they could set up and be safe, secure, and impenetrable. And I think we hit that on the head.”

Inspired by the arches and vaults of the older subway stations situated around Grand Central, the 4,000-square foot set paints a picture of an abandoned station-turned-repair shed that would have operated in the earlier part of the 20th century before being taken out of process in the 1920s. Butler’s crew purchased and transported an abandoned subway car from California and repurposed/rewired it to fit Finch’s needs.

The first thing to notice about the station: an almost uncountable number of doors. “They should give us plenty of places to arrive and depart throughout this season, and plenty of mysterious entrances and exits,” says Butler, adding that the design of the headquarters dovetails with a continuous conversation with Plageman and Nolan over what the characters will need to accomplish in the space. “Finch has the ability to transform household electronic equipment and computer systems to do pretty amazing things, so once we defined the space and located the train, we knew he would be adapting a combination of whatever was lying around from the 1940s and earlier with stuff he had brought from the surface. Every character has the supplies they need for their particular function.”

Something viewers might not notice immediately is the sheer expansiveness of the new headquarters. It’s a series of stations with “places where they can live, where they can stay underground for a long time, even an armory for Reese, all located somewhere in this labyrinth,” says Butler. And as for characters planning to spend the night? “There’s an emergency cot, but as of yet, nobody’s sleeping over…and nobody is sleeping together. But you didn’t hear that from me!”

There’s one last bit of design that Butler is particular proud of. Though viewers may never know the difference, Butler recreated nine replica period chandeliers and 24 wall sconces/brackets based on the original New York City lighting at the turn of the 20th century. Butler explains, “We took original gaslight fixture designs and electrified them—each light source is protected by a cage so you wouldn’t catch on fire. We built these forty some-odd fixtures, electrified them so they would illuminate the set and we could control them with dimmers and switches, but kept the period character of the old gaslight and had a lot of fun with that. It’s probably my favorite detail.”

While the library held its own elaborate secrets, Nolan and Plageman predict the new subway hide-out will hold stories of its own. “Finch has not found this place by himself,” says Nolan. “This place has been gifted to him by the Machine, whose larger purpose for them being in this location may not yet have been revealed.” Additionally, the technical trouble that comes with disappearing will be explored for the season’s first five (or so) episodes. “We definitely encounter some obstacles in terms of communication and access to resources,” says Plageman. “You’ll see how the Machine is gently nudging Harold Finch and all our guys towards finding ways to lead this insurgency against Samaritan in this new environment.”

With the new headquarters in place, it’s natural to wonder whether some of Team Machine’s missions will even take place entirely underground. “I’m absolutely sure that during the season there will be more opportunities in which subterranean stories may unfold,” teases Nolan. “Not a season goes by in which at least one of our writers hasn’t pitched a mole people episode. Who knows? We may finally get to that.”

They’ll have plenty of time, as their new subway home isn’t just a temporary pitstop. From the sound of it, Team Machine isn’t going back above ground anytime soon. “We just built the set,” laughs Plageman. “I think we’re going to get our money’s worth.”